1. Field of the Invention
The present invention relates to a disk drive apparatus for writing and reading data by emitting laser light onto a signal recording surface of a recording medium having a plurality of signal recording surfaces which form a layered structure.
2. Description of the Related Art
As optical disk recording media, CD-type disks, such as those commonly called xe2x80x9cCD-ROMsxe2x80x9d, and disks called xe2x80x9cDVDsxe2x80x9d (Digital Versatile Discs/Digital Video Discs) suitable for multimedia applications have been developed.
In disk drive apparatuses which use these optical disks, data is read by emitting laser light onto tracks on a disk rotated by a spindle motor from an optical pickup and by detecting the reflected light therefrom, or data is written by emitting laser light modulated by writing data onto tracks of a disk.
In order to perform a writing or reading operation by using laser light, the spot of the laser light must be maintained focused on a recording surface of the disk. For this purpose, in the disk drive apparatus, a focusing servo mechanism is provided for controlling the focus by moving an objective lens, which is at the output end of the laser light, toward or away from the disk. This focusing servo mechanism is conventionally formed of a two-axis mechanism having a focusing coil to move the objective lens toward and away from the disk and a tracking coil capable of moving the objective lens in the radial direction of the disk, and formed of focusing servo circuitry for generating a focusing error signal (i.e., a signal indicating the amount of difference from the focused state) from the information in the light reflected from the disk, generating a focusing driving signal in accordance with the focusing error signal, and applying the focus driving signal to the focusing coil of the two-axis mechanism. That is, the focusing servo mechanism is formed as a feedback control system.
Also, as is already well known, the range over which the spot of the laser light is brought into a focused state in accordance with the focusing error signal is in a very narrow range in which an S-shaped curve is observed as a focusing error signal. Consequently, in order to satisfactorily perform focusing servo, generally, an operation called xe2x80x9cfocusing searchxe2x80x9d is required as an operation for turning on a focusing servo loop.
In this focusing search operation, a focusing driving signal is applied to a focusing coil so that the objective lens is forced to move within the focusing stroke range thereof. At this time, while the focusing error signal is being detected, when the position of the objective lens is within a particular range, an S-shaped curve is observed. The focusing servo is turned on at the timing (or at the zero-crossing timing) at which the S-shaped curve is linear.
Some types of disks have a plurality of recording surfaces which form a layered structure. For example, in the case of the above-mentioned DVD, two signal recording surfaces, which are generally called xe2x80x9clayer 0xe2x80x9d and xe2x80x9clayer 1xe2x80x9d, are formed.
The structure of a DVD having two signal recording surfaces is shown in FIG. 14. The DVD is a disk having a diameter of 12 cm, and the thickness of the disk is 1.2 mm, as shown in FIG. 14.
In the layered structure of this DVD, first, a disk substrate (transparent layer) 101 of a synthetic resin material, such as a transparent polycarbonate resin, a polychlorinated vinyl resin, or an acrylic resin, having a high light transmittance and mechanical resistance characteristics or chemical resistance characteristics, is formed on a disk surface 108.
Pits are transferred to the disk substrate 101 by a stamper having a molding die incorporated on one of its main surfaces, forming a first signal recording surface 102. The pits on this first signal recording surface 102 are formed, as small coded holes whose circumferential lengths differ from each other in accordance with a predetermined information signal, on the disk substrate 101, forming recording tracks.
Furthermore, a second signal recording surface 104 and a second reflection layer 105 corresponding to the second signal recording surface 104 are formed via a first reflection layer 103 corresponding to the first signal recording surface 102. The second signal recording surface 104 is also formed with pits corresponding to an information signal in a manner similar to that for the first signal recording surface 102.
A bonding surface 106 is formed on the second reflection layer 105, and a dummy plate 107 is bonded via the bonding surface 106.
Laser light from the disk drive apparatus is made to enter the DVD from the disk surface 108, and information recorded on the first signal recording surface 102 or the second signal recording surface 104 is detected from the reflected light therefrom.
More specifically, the first reflection layer 103 is formed into a semi-transparent film so that a fixed ratio of laser light is reflected. As a result, if the laser light is focused onto the first signal recording surface 102, it is possible to read a signal recorded on the first signal recording surface 102 from the light reflected by the first reflection layer 103. Also, when the laser light is focused on the second signal recording surface 104, the laser light passes through the first reflection layer 103 and is focused on the second signal recording surface 104, making it possible to read a signal recorded on the second signal recording surface 104 from the light reflected by the second reflection layer 105.
For a disk having a plurality of signal recording surfaces, such as a DVD with a two-layered structure, it is necessary for the focusing servo mechanism to focus the laser light onto the respective signal recording surfaces. In other words, when the laser light is focused on one of the signal recording surfaces, it is necessary that an operation for changing the focus onto the other signal recording surface, that is, a focusing jump operation, can be performed.
This focusing jump operation is performed by forcing the objective lens to move while the focusing servo is turned off when a focused state is reached on one of the signal recording surfaces and by turning on the focusing servo when the laser light reaches in a focusing pull-in range for the other signal recording surface (i.e., when the S-shaped curve is observed). That is, this is an operation similar to that in the above-described focusing search operation.
When such a focusing jump is t o be performed, by considering a surface wobbling of the disk, influences of external disturbances are reduced by moving the objective lens at an acceleration larger than the wobbling acceleration thereof.
However, in a disk having a large degree of wobble, the focus position of the objective lens must be displaced greatly within the rotation cycle of the disk. Therefore, in order to perform a focusing jump operation with respect to a disk having a large degree of wobble, it is necessary that complex servo control be performed in which the rotation speed and the amount of wobble of the disk are taken into consideration.
In order to solve these problems, in one aspect, the present invention provides an apparatus for writing and reading data by emitting laser light on each signal recording surface of a recording medium having a plurality of signal recording surfaces, the apparatus comprising: a pickup device having an objective lens which is at an output end of the laser light; an objective lens moving device for setting the focused state of the laser light with respect to the signal recording surface of the recording medium by moving the objective lens toward or away from the recording medium; a detection device for detecting moved distance information indicating the relative distance moved between the objective lens and the signal recording surface; and a focusing jump control device for controlling the objective lens moving device so that a focusing jump operation is performed for moving the focus position of the objective lens from the current signal recording surface to another signal recording surface, wherein the focusing jump control device performs the focusing jump operation at a position where the relative distance moved with respect to the recording medium is not more than a predetermined value.
In another aspect, the present invention provides an apparatus for writing and reading data by emitting laser light on each signal recording surface of a recording medium having a plurality of signal recording surfaces, the apparatus comprising: a pickup device having an objective lens which is at an output end of the laser light; an objective lens moving device for setting the focused state of the laser light with respect to the signal recording surface of the recording medium by moving the objective lens toward or away from the recording medium; a detection device for detecting moved distance information indicating the relative distance moved between the objective lens and the signal recording surface; a focusing jump control device for controlling the objective lens moving device so that a focusing jump operation is performed for moving the focus position of the objective lens from the current signal recording surface to another signal recording surface; and a storage device for storing the moved distance information within a predetermined period, wherein the focusing jump control device controls the objective lens moving device in accordance with moved distance information stored in the storage device and a driving signal for a focusing jump operation.
In another aspect, the present invention provides apparatus for writing and reading data by emitting laser light on each signal recording surface of a recording medium having a plurality of signal recording surfaces, the apparatus comprising: a pickup device having an objective lens which is at an output end of the laser light; and an objective lens moving device for setting the focused state of the laser light with respect to the signal recording surface of the recording medium by moving the objective lens toward or away from the recording medium, wherein the objective lens moving device moves the focus position of the objective lens from the current signal recording surface to another signal recording surface by maintaining the current position of the objective lens while maintaining the level of a driving signal for moving the objective lens.
According to the present invention, when data is read from a disk with a plurality of signal recording surfaces in a layered structure, stable focusing jumps can be performed.
The above and further objects, aspects and novel features of the invention will become more apparent from the following detailed description when read in connection with the accompanying drawings.